Process for separating cooking liquor from pulp



Dec. 19, 1950 P. G. VON HILDEBRANDT 2,534,324

PROCESS FOR SEPARATING COOKING LIQUOR FROM PULP 4 Sheets-Sheet 1 Filed July 2, 1945 gvvua/wbo v M Raw. 6 v0 H/L EBRANDT d 4 Momm Dec. 19; 1950 P. G. VON HILDEBRANDT PROCESS FOR SEPARATING COOKING LIQUOR FROM PULP 4 Sheets-Sheet 4 Filed Julx 2, 1945 F i9 INVENTOR.

Pivon Hflafiebranaf B 2 V W ATTORNEY Patented Dec. 19, 1950 OFFICE PROCESS FOR SEPARATING COOKING LIQUOR FROM PULP Paul G. von Hildebrandt, Port St. Joe, Fla.

Application July-2, 1945, Serial No; 602,898:

8' Claims. 1

This invention relates. to a-processzand apparatus. for separating pulp from cooking liquor in themanufacture of paper. A principal objectof theinvention is to providea. processand apparatus ofthe character designated by meansof which the major portion-.oflthe cooking liquoris recovered without water. dilution.

A further object of my invention .is toprovide a process andapparatus in-which the cooking liquor is separated from .the .pulp by, passing. currents of a steam. through. the pulp, thereby. maintaining theresinsandlignins in a fluid condition.

Astill further object ofv my invention isto provide a process andiapparatus. in which the cooking liquor is separated from ulp witha minimum ofwater dilution, thereby reducingthe: foaming and the heat required forevaporatingthe black liquor down for. subsequentlburning.

A still further object of my invention is toprovide apparatus for separating. pulpfrom cooking liquor which shallinclude means. for employing steam asthe separating agent.

Arnore specific object of my invention is the provision of apparatus for separating cooking liquor. from pulp which shall includeablOw tank through which the pulpmoves continuously, having the major portion of the liquorseparated therefrom while in transit, without theuse of wash water, therebyminimizing.foaming and the pulp from the digesters, difiiculties havebeen encountered in theloss of 'pulp' with theescaping steam. In" the diffuser type of separator, the black liquoris drained through a perforated bottom on which'the pulp is retained, and weak liquor issupplied to the mass ofi-pulp; to displace and wash the. stronger black liquor from the fibers until the liquor'has reached its' minimum density. Hot-wateris'then used to continue the washing of. the liquor from. the fibers. In the vacuum type of pulp washing machine, there is a rotary perforated metal cylinder covered'with a fine'mesh wire'screen which is'partly submerged and rotated in a mixture of pulp and black liquor. The inner sideof the cylinder is connected to. a-suction deviceand during a part of each revolution alayer of pulp is drawn onto the screenandthe black liquor is filtered out. During a further part of the-revolution, hot water showers drenchthe mat of fiber on the drum and this wash water isalso drawn through the screen. The mat of pulp is then washedoff the screen withpowerful jets of water into a stock chest.

With either of these methods, a great deal of water is employed and the b'lack liquor is greatly diluted. As is also well known, it is the practice to evaporate. the black liquor down to a consistency where it canbe economically employed asafuel andzthen it is burned in the boiler furnaces -0f the mill to supply heat and to recover the chemicalsused incooking the wood chips. The heat required to evaporate the black liquor downis expensive and it is the principal object of my invention to provide a process and apparatus which will recover the black liquor with a minimum of dilution.

In accordance with my invention, I provide a blow tank of the necessary capacity to take care of the pulp as it is cooked. The digesters are discharged into this blow tank through a cyclone having a weighted valve in the bottom through which thepulp passes downwardly into the tank. The tank is provided witha perforated, screened conical bottom through which the black liquor drains into astorage'tank. At the lower end of the'conical bottom, is disposed a screw conveyor which removes-thepulp as itreaches the bottom of 'the tank. The conveyor is provided with a perforated trough through which the liquor continuesto drain. While-in the conveyor, steam is diffused through the pulp which maintains the lignins'and resins in a liquid condition so that they are expelled from the pulp responsive to the squeezing action of the conveyor screw. This is'very important in separating the black liquor from the knots which in practice absorb the greater proportion of the black liquor. A plurality of screw conveyors are preferably employed, each of which has an increasing diameterfrom its inlet to its discharge end whereby to allow for the expansion of the pul as it is separated from the black liquor, and to provide for betterdiffusion of the steam through the pulp. Other'featuresofmy invention consist in means to prevent' the carrying over-of pulp with the steam from the black liquor as it is discharged from the digester and in the various details of construction and arrangement of parts hereinafter described.

Apparatus embodying features of my invention is illustrated in the accompanying drawings, in which Fig. 1 is an assembly view showing the apparatus for carrying out my invention;

Fig. 2 is a detailed sectional view of the cyclone through which the pulp-black liquor is blown into the blow tank, and taken along the line 11-11 of Fig. 1;

Fig. 3 is a sectional view of the blow tank and showing in section the screw conveyor connecting with the lower end of the tank;

Fig. 4 is a view taken at right angles to Fig. 2 and showing one of the screw conveyors in section;

Fig. 5 is a sectional view taken along the line VV of Fig. 3;

Fig. 6 is a sectional view taken along the line VI-VI of Fig. 3;

Fig. 7 is a sectional view showing the manifold and bafiie arrangement through which the steam from the black liquor is discharged;

Fig. 8 is a sectional view taken along the line VIII-VIII of Fig. '7;

Fig. 9 is a plan view of the screw conveyors;

Fig. 10 is a side elevation thereof with parts broken away;

Fig. 11 is a sectional View taken along the line XI-XI of Fig. 9; and

Fig 12 is a sectional view typical of the three conveyors showing the means for admittin steam to the pulp.

Referring now to the drawings for a better understanding of my invention, I show in Fig. l a paper mill installation comprising a digestor H], a blow down line H, connected to the digestor, and discharging into a cyclone l2. From the cyclone l2, the black liquor and pulp pass downwardly, with a whirlin motion, into my improved blow tank is wherein the black liquor is separated and flows into a storage tank 14,

The pulp is removed from the blow tank by means of a system of screw conveyors I6, I! and 18. The cyclone I2, is provided with a tangential inlet I9, and a bottom outlet 2! in which is located weighted trap valves 22, and 23 which open responsive to the weight of pulp and black liquor on them allowing it to pass downwardly through the discharge opening 2| in the blow tank 13.

Mounted above the cyclone I2 is a baffle chamber 24, shown in detail in Fig. 7. The bailie chamber 24 has its Wall 38 provided with a multiplicity of downwardly inclined, overlapping baiiles 26. It is open at the bottom and top as shown in Fig. '7 and has connected to the upper end a discharge conduit 21. Steam from the pulp and. black liquor being discharged from the digestor 10, passes upwardly through the balile chamber, the bafiies 25 serving to intercept any pulp being carried over with the steam and to return it to the cyclone 52. There is thus no loss of pulp due to bein carried over by the steam. Surrounding the baffle chamber 24, is a manifold 28 having a lateral connection 23. The wall 36 is perforated as shownat 3!, within the manifold 28, whereby liquor or steam may be admitted when required through the connection 2?! and pass through the perforations and over the baffles to wash and remove any accumulation of pulp thereon.

The blow tank 53, as shown in Fig. 3, comprise a cylindrical inner shell 33, made of steel plate and is provided with a conical bottom 34. At the bottom is an openin 36, through which the pulp is discharged. The inner shell 33, is made of steel plate and is perforated for approximately three-fourths of its height from the bottom with relatively large perforations 31. Fitting within the shell 33, are relatively thin gauge plates 38, having relatively fine perforations, forming a screen. These plates are preferably made removable by an suitable means, not shown, whereby they may be changed when required. The upper end of the inner shell 33, has connected thereto a conduit 39, leading to a safety valve 4!, for the relief of excess pressure within the inner shell. Also, at 42 is shown a conduit leading to a pressure gauge 43. After the digester is blown and the inner shell is full. pressure accumulates due to the contained heat of the liquor and pulp. This pressure aids in draining the liquor from the pulp through the screens. The connection to the cyclone I2, is made by means of a frusto conical outlet connection 454, terminating in a flanged Opening 45, which connects with the flanged outlet 23 of the cyclone. This frusto conical connection 44 aids in distributing evenly the incoming pulp around the inner shell 33 and in throwing out liquor.

Surrounding the lower perforated portion of the inner shell 33 is an outer shell 4! having its upper end joined to the inner shell at 48, as by welding. The outer shell 4! is generally cylindrical in shape and is connected to the storage tank l4 by means of a flanged connection 49. At 5! I show a manifold extending vertically alongside the outer shell Ill, and connected to the manifold are a plurality of conduits 52, 53, 54, 5B, 57, 58, 59 and 5!. The conduits 52, 54 and 5'! to SI inclusive extend through the inner shell 33, and connect to headers 52, which lie closely adjacent the inner Wall of the shell 33, and are provided with downwardly directed jets 63, through which liquor, as desired, may be discharged. The conduits 53 and 55 terminate in headers 64 which surround the outside of the inher shell 33, lying closely adjacent thereto, and are provided with downwardly directed jets 66.

Connected to the discharge openin 36 at the lower end of the inner shell 34 is an upwardly inclined trough or jacket 31 for a screw conveyor having a tapered screw 69 which increase in diameter from the lower end where the conveyor connects to the discharge opening to its upper, discharge end. The lower half of the trough 6'! is provided with perforations H, through which black liquor removed from the pulp by the action of the conveyor, drains downwardly into the storage tank l4. Outside the shell 4'! there is an outer housing 12, which is joined to the trough 61, at 13, above the perforations ll. See Fig. 6. The housing 12, is connected by means of a flanged connection M to the outer shell 41, and communicates with the inner shell 41, through an opening 16. Inside the shell 41, the trough 6! is provided with a cover 11 which sheds any black liquor falling downwardly from the conical bottom 34, above it. See Fig. 5. The screw 69 is mounted on a hollow sleeve 18, which is mounted on a shaft 19. Steam may be admitted to the sleeve '58 through a rotary steam joint 80. Steam admitted through joint passes into the sleeve and from thence is diifused through the perforations into the pulp within the conveyor trough 61. The conveyor is driven by means of a variable speed motor 8| and a suitable train of gearing 82.

assesses The upwardly inclined 'conveyor trough=- Ii I is 'provided -w'ith a dischargeoutlet 8-3 "which com:- "municates with the' 'trough *84 of a; horizontal-y 'disposed screw' conveyor: The' trough 84 com- "municates withthe upper end of the housing 1 2,

and' is "provfded "witl'i perforations 86'; sdthat liquor separated from the pulp in the horizontal conveyorma'y draininto the housing 1 2; The horizontal conveyor is" provided with a tapered "screw=- 815 which gradually-increasesin diameter from" its connection tothe inclined*'conveyor 'to'- ward the dischargeendf The screw =81 is'"d'riven by means of a shaft' afli having mounted thereon or'surroundi'rrg which-'is a perforated sleeve 89.

"steam'admitteu through'the sleeve"89, as'al'ready described," is diffused-into" the pulp *b eir'ighandld byth'e conveyor. Cbnnectedtd-the lower" half ofth'e housing," or trough li lkis housing 9"I similarto the liousi-ng-Hf for the inclined conveyor,

and'whicli'connectsto airopeninginto the housing 12? The-housing 9-1; is joined t'o'th'e trough Bl, above-the'perforations st,

posed conveyor which conveys 'it upwardly; The

receptacle 9 la -istprov-idedswith aeperforated bottom and drains into the housing 9|. The ver- .tically" disposed conveyor" is providedv with. a tapered screw"91"similar"to" the screws: described in connection with the other "conveyorszandili'n- 5 creases" inniameter from the Iower to the upper,

discharge end. "Surrounding. the. screw. .91 isa perforatedljacket"99"tlirough which liquor is discharged into a surrounding imperforate housing IIII and passes downwardly-through a lateral conduitallios into the housing 9|; The housing I'M isrjoinedrat its upper end at-- Hi2 Withf'ak'fluld tight 'connection to the jacket-99. The-:pulp is finally discharged from the upper end of the vertical conveyor through a discharge opening I03, from whence it may be conveyed in any suitable manner for further processing as is well understood. The vertical conveyor, similarly to the upwardly inclined and horizontal conveyors, is driven by a separate variable speed motor I04, through a suitable gearing I06.

All of the liquor removed from the pulp in my improved blow tank, drains downwardly into the storage tank I4. The latter is provided with a heating coil I01, supplied with steam from any suitable source through a connection I08. The liquor is thus maintained in a free flowing, nonviscous condition.

Condensate is removed from the coil IIl'I through a trap I09. Liquor drained into the storage tank I4 is removed by means of a pump I I I, which discharges through a conduit II2. A strainer is preferably interposed between the tank I4 and the pump I I I. As is well understood, the black liquor is then filtered and evaporated down to the proper density for burning.

When the apparatus is shut down it is desirable that the inner shell be thoroughly washed of any retained fiber. For that purpose, I show a conduit II 3 connected to the discharge conduit IIZ. By opening a valve H4 in the conduit H3 and closing a valve H5 in the conduit II2, black liquor is delivered to the manifold 5| and is discharged through the nozzles 63 and 66 6 against ther inner and" outer' 'si'deszof; the. inner sliell 33.

The manifold 5I is' providediwithz :steam'tsupi ply througli -a. .steam supp1y;i conduit-Z Hi3, whereby steami 'mayfbei employedzwith the .blacksiliquor, or" alone, in cleani-ng out thex-system'. At the upper end of the:manifoldial ,.Lprovide :a: valve [1 Ticonnected to -a conduittIIfii which leadsi' to the connection 29, on the manifold 28. .Aicheck valve: Il adja'oentthe :connectionIZ'Brpreventsithe blowing-wash of 'steam when'ithexdi'gester is cbeiing: discharged into. the:blow tank. Blackrliquor together with steam from: the conduit II3f'may be: admitted into the manifold 5 I through'ithe valve I M "andl from thence through the conduit H81 and: perforations' 3il tocleamthe .baiiies 26, as already described.

From the foregoing descriptiomLthe.operation .ofi mi -"improved apparatusiwill be readily: understood. Thexc'ontents of the digester." III; at:.the end iof 'a cook;. and consisting? ofsblack liquorun- .d'erpressure; with thebatch. of chips,. is blown .through'athablovw linei'II. into the cyclone; I2 where: the. (steam: is separated from v the i liquor and pulp and'passes' out. through the discharge :conduitufl. Any: pulp-inzthe steam is separated out by means of the baffles 26, in the 'bafiie' chamberz h. The: black liquoivandipulp-pass downwardly with azwhjrlingi motion through the strap valves; 22cand123 into the'i'nner shelln33 where itiis "evenlyrdistributed about theishell... Thexhlack liquor passes out through thei screened, perforated l'ower end: of: the inner shell: and drains downwardly intoztherstorageitank It. When :the inner shell is full, above the perforationssteam a'ccumulateszabovee thermassi and a-idssin forcing thezblacle liquor: outithroughither perforations:

aThei'pulp settles by' 'gravityfinto the 'lowervend ofthevzconical. bottom 34, .andtpasses into the lowerrendxof. the upwardly inclined conveyor troug'h :Ii'1;,and* is:' conveyed upwardly therefrom byftliertaperedrconveyor' screw andiisdischarged into: theshorizonta'l: conveyor trough 84 From thence it" is: conveyed". horizontally to the vertical conveyor housing-.i'an'dvis then carriedsupwardly to be discharged through the discharge chute I03. In its passage through the conveyors, saturated steam at a temperature of from 250 to 280 F. is diffused through the pulp by means of the perforated sleeves surrounding the shaft' so that it is maintained in a heated condition at all times and the black liquor with its resins and lignins is forced out therefrom through the perforated troughs of the conveyors. The speed of the conveyors is regulated to provide the maximum recovery of black liquor from the pulp with a minimum expenditure of steam.

In actual practice I have found that black liquor, after separating the pulp in accordance with my invention hereinbefore described and with all necessary wash water added has a specific gravity of from 13 to 18 B. as compared with a specific gravity of from 3 to 7 B. when separated by prior art methods. It thus requires around 40% less heat to evaporate it down to a consistency suitable for burning and recovery of the chemicals therein. By this means, I am enabled to separate from 85 to per cent of the black liquor from the pulp without material dilution. The steam diffused through the pulp is in part condensed, providing a small amount of liquid which aids the steam pressure in forcing the black liquor and suspended solids from the pulp. In my improved method there is no foaming in the separation of the liquor due to the absence of added water and agitation. I thus avoid the addition of antifoaming agents which weaken the fiber and are expensive.

From the foregoing, it will be apparent that I have devised an improved process and apparatus for the separation of cooking liquor from pulp in the manufacture of paper in which the cooking liquor is separated with a minimum of dilution.

While I have shown my invention in but one form, it will be obvious to those skilled in the art that it is not so limited, but that it is susceptible of various changes and modifications without departing from the spirit thereof, and I desire, therefore, that only such limitations shall .be placed thereupon as are specifically set for h pulp in the manufacture of paper which comprises draining the liquor from the pulp while allowing it to settle into a progressively diminishing confined space, and then subjecting it to a squeezing action while draining and while moving it toward a progressively larger confined space.

4. A method of separating cooking liquor from pulp in the manufacture of paper which comprises draining the liquor from the pulp while allowing it to settle into a progressively diminishing space, then subjecting it to a squeezing action while draining and While moving it toward a progressively larger confined space, and during said draining diffusing saturated steam through the pulp to maintain the resins and lignins in a heated condition.

5. A method of separating cooking liquor from pulp in the manufacture of paper which comprises passing the mass of liquor containing pulp through a succession of screened enclosures and diifusing steam from within the mass outwards to maintain the lignins and resins in a heated condition. y

6. The process of separating cooking liquor from wet pulp in the manufacture of paper which comprises diffusing steam from the interior of a confined mass of said pulp outwards while draining the liquor from said mass.

'7. The process of separating cooking liquor from Wet pulp in the manufacture of paper which comprises diffusing steam from the interior of a confined mass of said pulp outwards while draining the liquor from said mass and while moving it toward a progressively larger confined space.

8. The process of separating cooking liquor from wet pulp in the manufacture of paper which comprises diffusing steam from the interior of a confined mass of said pulp outwards while draining the liquor from said mass and while gradually increasing the bulk of said mass.

PAUL G. VON HILDEBRAN'DT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,567,663 Mosebach Dec. 29, 1925 1,860,836 Gustin May 31, 1932 1,933,609 Wagner Nov. 7, 1933 2,063,367 Roza Dec. 8, 1936 2,355,091 McDonald Aug. 8, 1944 2,360,779 Lang Oct. 17, 1944 FOREIGN PATENTS Number Country Date 52,852 Norway July 24, 1933 331,267 Germany Jan. 5, 1921 

1. THE PROCESS OF SEPARATING PULP FROM COOKING LIQUOR IN THE MANUFACTURE OF PAPER, WHICH COMPRISES DIFFUSING STEAM THROUGH A MOVING MASS OF SAID PULP AND DRAINING THE LIQUOR FROM SAID MASS. 